1. Field of the Invention
The present invention relates to a process for wet carbonizing of peat.
2. Description of the Prior Art
Wet carbonizing of peat implies chemical decomposition of raw peat, which takes place in liquid phase at temperature about 200.degree. C. under pressure, and during which reaction carbon dioxide, water and certain organic impurities are split off from the peat dry substance. Hereby the carbon content of the dry substance increases, and it loses its gel-resembling structure, whereby it becomes possible to remove water mechanically by filtering and pressing from the wet-carbonized peat suspension to such degree that the press cake will have a dry matter content up to 50%. After thus the major part of the water has been mechanically removed from the wet-carbonized peat suspension, an essential part of the residual water content may be removed by thermal drying.
The product thus prepared, that is dry wet-carbonized peat, is mainly used as fuel in energy producing or as raw material for further conversion in to products--such as peat cokes for instance--in which also the energy content plays a remarkable role. Decisive significance with regard to the economy of a wet carbonizing plant attaches to an exhaustive heat recovery in the process, since optimum energy economy also gives an optimum energy yield.
At the same time, naturally, the losses of dry substance from the process to the environment should be minimized.
In proposals for wet carbonizing plants existing in prior art, the heat recovery has been partly taken into account. For instance, the company Ab Svensk Tor vforadling shows in a stencilled report of the year 1960 how it is possible with the hot peat suspension flowing from the wet carbonizing reactor to preheat the raw peat suspension flowing to the reactor, and also how the hot filtrate obtained from the filter presses can be utilized towards preheating the raw peat suspension. However, in this plant description one has failed to connect a steam boiler required in the plant, on the flue gas side, with a thermal drying means for the drying of the wet carbonized peat, nor has any other such heat recovery from the exhaust gases of the steam boiler or of the separate drying means been planned which would have any influence on the heat economy of the wet carbonizing plant itself.